1. Field of the Invention
This invention relates to a metal diffusion barrier of insulating material and in particular, but not exclusively, to barriers which limit the diffusion of copper into an insulating layer.
2. Background of the Invention
It is well known, in the manufacture of semiconductors and similar devices, that if a metal, such as copper, has a direct interface with an insulating material such as silicon dioxide, then, particularly when the metal atoms are energetic under heating or when current is passed, those metal atoms diffuse into the insulating layer and can set up a conducting short circuit between wiring lines and the like. The likelihood of such occurrences increases as the dimensions of the architecture of the devices decreases.
It has been known for some time that the way to overcome this problem is to deposit a barrier layer between the metal and the insulating layer. However, many of the usual candidates, such as silicon nitride, significantly increase the capacitance created by the insulating layer as a whole which is undesirable.
WO00/19498 proposes the use of a SiC material as a barrier layer, but the materials suggested all have a dielectric constant of over 4 and indeed 4.2 seems to be the best value reported for the barrier layer.
EP-0725440 also suggests the possibility of silicon carbides being used as diffusion barriers or having the silicon carbides as the insulating layer themselves. The specification is however very short on description and is confused about the dielectric constants involved. However, in its plainest statement, it would appear that the dielectric constant of the silicon carbide is nearer 5 than 3.5.